I have a latent growth curve model with two growth curves of respectively cognitive development and motor development. The intercepts and slopes of both growth curves are correlated. My problem is that cognitive development is measured on an interval scale while motor development is a dichotomous variable (whether a child performed a certain movement or not). Is it possible to estimate both growth curves in one model?

Thanks for your swift reaction. When I've defined the variables as categorical, could I then best use the WLSMV estimator (I assume default would be ML)? My sample size is rather small (74 for each occasion).

The default is WLSMV. You can ask for maximum likelihood using the ESTIMATOR option. You can do a Monte Carlo study to see if your sample size is sufficient. With repeated measures, the sample size can be smaller than with cross-sectional data. See the following paper: